| 摘要 |
PURPOSE: To make the structure of a picture projector compact by arranging transition structure so that either a 1st light beam or a 2nd light beam may be totally reflected and the other may be transmitted. CONSTITUTION: An angle dependent type beam splitter having the shape of a composite prism element 5 is used to properly separate the beam to the beams b1 and b2 at the part of a projection lens system 20. The element 5 is equipped with two transparent prisms 6 and 7 made of glass or synthetic resin material, and an air layer 8 is formed between the prisms in the element 5. Since the refractive index nm (for example, nm is 1.5) of the material of the prism is larger than the refractive index(n1 =1.0) of air, the beam made incident on a boundary between the prism and the air at an angleθi larger than or equal to a critical angleθ9 is perfectly reflected on the boundary. Meanwhile, in the case the light beam is made incident on the boundary at the angle smaller than the critical angle, it is perfectly transmitted. Thus, the projection lens system 20 is positioned proximately to a display panel 10, and the picture projector is made compact than in the case it has no prism system.
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